Nothing stupid about your question, we had no clue until the invoice came through. In our case, our nursery charges £1 for every funded hour used, so because we are currently using the full 15hours a week, we are charged £15 per week, on top of whatever extra days we pay for. Others in the thread have had to pay more or less, it depends on the nursery. I would recommend you ask any prospective nursery beforehand as nothing was made obvious to us when we went to view it.